Exhaust systems are widely known and used with combustion engines. Typically, an exhaust system includes exhaust tubes that convey hot exhaust gases from the engine to other exhaust system components, such as mufflers, resonators, etc. A muffler includes acoustic chambers that cancel out sound waves carried by the exhaust gases. Although effective, mufflers are often relatively large in size and provide limited nose attenuation.
Passive valves have been used in a muffler to provide further noise attenuation. However, the proposed valves have numerous drawbacks that limit their widespread use in a variety of applications. One disadvantage with passive valves is their limited use in high temperature conditions. Another disadvantage with known passive valve configurations is that these valves do not effectively attenuate low frequency noise.
Attempts have been made to improve low frequency noise attenuation without using passive valves by either increasing muffler volume or increasing backpressure. Increasing muffler volume is disadvantageous from a cost, material, and packaging space perspective. Increasing backpressure can adversely affect engine power.
One solution is to locate the passive valve outside of the muffler. An example of such a configuration is found in applicant's co-pending application Ser. No. 11/950,034 filed on Dec. 4, 2007. While this solution has proven to be effective, other challenges are presented within the overall exhaust system by this type of mounting arrangement. A position of the passive valve in relation to other exhaust system components becomes an important characteristic from a noise reduction perspective. A specific position of the passive valve in the overall exhaust system is directly tied to the acoustic effectiveness of the valve. For example, positioning the valve at an acoustic velocity nodal point is ineffective.
Additional challenges are also presented by multi-exhaust component systems, such as systems that include more than one muffler for example. Positioning the passive valve in front of a main muffler can give rise to chatter issues due to a higher level of pressure pulsations.
Therefore, there is a need to provide an exhaust system and passive valve arrangement that can effectively attenuate low frequency noises without introducing other types of noise issues. This invention addresses those needs while avoiding the shortcomings and drawbacks of the prior art.